If a magnetic random access memory (MRAM) or a dynamic random access memory (DRAM) is miniaturized, a contact area between a source/drain diffusion region of a MOS transistor and a contact plug is decreased. Consequently, the contact resistance between the source/drain diffusion region and the contact plug is increased, which adversely affects device operation.
Therefore, what is desired is a semiconductor device in which the resistance in a source/drain diffusion area can be reduced.